She studied at the Pasadena Playhouse (1964–1965). She appeared in You'll Like My Mother (1972), starring Patty Duke, Rosemary Murphy and Richard Thomas. For this role, Allen was nominated for the 1973 Golden Globe Award as Most Promising New Actress.

She married and had a daughter. Her own mother and father divorced around 1965. She is the older sister of flash fiction author, Editor and Teacher Meg Pokrass.

She later garnered fame on two episodes of The Waltons (1973) as Jenny Pendleton, an early love interest of John-Boy Walton (reuniting her with Thomas, who played John-Boy and with whom she had appeared in You'll Like My Mother the previous year). Allen and Thomas were themselves described as "together these days", and Thomas wanted Allen to play the Pendleton role. She played the title role in the 1973 ABC Movie of the Week, Scream, Pretty Peggy.

Allen appeared on television programs such as Captains and the Kings, The Incredible Hulk, Ironside, The Rockford Files, Alias Smith and Jones, Bonanza, Kojak, Gunsmoke, Love, American Style, Columbo: Lovely but Lethal, Cagney & Lacey, Adam-12, and Hawaii Five-O. In 1974 she was the lead Actress in the western Billy Two Hats, alongside Gregory Peck and Jack Warden. In 1976, she portrayed Anne Morrow Lindbergh in the television movie The Lindbergh Kidnapping Case, based on the real-life Lindbergh baby kidnapping/murder. Her last role was in an episode of L.A. Law in 1990, after which she retired from acting.